With advancement of wireless communications in terms of increased speed and capacity and advancement of wireless devices in terms of reduced size, there is an increasing demand for antennas operating in a millimeter wave band (30 GHz or more and 300 GHz or less). It is important to design an antenna operating in a millimeter wave band so that a conductor loss and a dielectric loss may be suppressed, because a conductor loss and a dielectric loss increase as frequency becomes higher.
A waveguide tube is preferable as a transmission path for transmitting an electromagnetic wave in a millimeter wave band. A comb-line microstrip antenna is preferable as an antenna for radiating an electromagnetic wave in a millimeter wave band.
Patent Literature 1 discloses a comb-line microstrip antenna. Patent Literature 2 discloses an antenna in which a waveguide tube is attached to a comb-line microstrip antenna.